Lizards Sceloporus Jarrovii Research Articles

Diet of the Yarrow's Spiny Lizard Sceloporus jarrovii in the Central Chihuahuan Desert

We studied seasonal dietary patterns of Sceloporus jarrovii from a desert environment northwest of Gomez Palacio, Durango, Mexico. Stomach contents were examined (n = 82) and relative abundance and volume were determined. Formicids (ants) were the most abundant prey in all seasons. Other abundant foods were coleopterans (summer, winter) and isopterans (autumn, winter). Based on relative abundance in all seasons, S. jarrovii had a narrow breadth of diet, but relative volume of foods was broader. Overlap between sexes for relative abundance and volume was high throughout the year. However, low overlap in relative volume in spring indicated variation in diet between sexes. Three of the most common prey throughout the year varied significantly between sexes in length, width, and volume. However, volumes of the three most abundant foods were not correlated with snout–vent length of lizards.

Predation risk, escape and refuge use by mountain spiny lizards (Sceloporus jarrovii)

AbstractEconomic theories of antipredatory behavior take into account expected fitness losses and gains to predict escape decisions. Prey at greater risk are predicted to have longer flight initiation distance (= distance from predator when escape begins), flee farther, be more likely to enter refuge, and have longer hiding time (= time between entering and exiting refuge). We simulated predators to study effects of risk factors in the lizard Sceloporus jarrovii. Flight initiation distance, distance fled and probability of entering refuge increased with approach speed. Flight initiation distance increased additively with increases in speed and directness of approach. Lizards habituated to human presence had shorter flight initiation distances than unhabituated lizards. As predicted from greater threat posed by a persistent predator, flight initiation distance and hiding time were longer after the second of two approaches. Fleeing was more likely when an investigator stood nearby and turned toward them than when farther way or turned away. These findings verify theoretical predictions of escape and refuge use for several risk factors and most are consistent with those for other lizards. However, speed and directness of approach had additive effects in S. jarrovii, but interacted in other species. Another novel finding was a small interaction between individual investigator and directness of approach. Although outcomes of tests of escape and refuge use theories consistently confirm qualitative predictions, quantitative comparisons between studies by different investigators may have limited value unless information is available about relative responses by prey to each investigator.

A test of optimal foraging and the effects of predator experience in the lizards Sceloporus jarrovii and Sceloporus virgatus

AbstractForaging efficiency of predators can be evaluated by using optimality or profitability models which incorporate prey choice, handling time and pursuit or search time. Optimality of a diet could vary based on the age, sex, size, predation risk, or foraging experience of the predator. This study tested the effects of a predator's age and foraging experience by observing prey capture attempts and success rate, and by calculating diet profitability for adult and neonate Sceloporus jarrovii and adult Sceloporus virgatus. Prey availability was assessed in order to determine prey preference and profitability. Neonates showed an increased number of prey capture attempts, but success rate was similar for neonates and adults of both species. Total diet profitability of neonates was lower than adults of either species, which could be a result of poor prey choice or gape limitation (although body size showed no direct effect). Overall, the diets of all three groups were less profitable than would be expected based on the types of prey in the environment, although this is likely due to low availability (from the lizard's perspective) of highly profitable items. Lizards seem to be eating prey items in the same proportion as they are found in the environment.

A test of the reproductive cost hypothesis for sexual size dimorphism in Yarrow's spiny lizard Sceloporus jarrovii

1. Trade-offs between reproduction and growth are central assumptions of life-history theory, but their implications for sexual size dimorphism (SSD) are poorly understood. 2. Adult male Yarrow's spiny lizards Sceloporus jarrovii average 10% larger than adult females. In a low-altitude (1700 m) population, this SSD develops because males grow more quickly than females during the first year of life, particularly during the first female reproductive season. This study tests the hypothesis that SSD develops because female growth is constrained by energetic costs of reproduction. 3. To test for a growth cost of reproduction, I compared growth rates of free-living females that differed, either naturally or experimentally, in reproductive status. Females that naturally delayed reproduction until their second year grew more quickly than females that reproduced as yearlings, and ovariectomized yearlings grew more quickly and to larger sizes than reproductive controls. 4. To determine whether SSD develops in the absence of this inferred reproductive cost, I also studied a high-altitude (2500 m) population in which all females delay reproduction until their second year. Sex differences in growth trajectories were similar to those observed at low altitude, such that males averaged 10% larger than females even prior to female reproduction. 5. Although female growth may be constrained by reproduction, multiple lines of evidence indicate that this cost is insufficient to explain the full magnitude of SSD in S. jarrovii. First, differences in growth of reproductive and nonreproductive females are not observed until the final month of gestation, by which time SSD is already well developed. Second, the growth benefit accruing from experimental inhibition of reproduction accounts for only 32% of the natural sex difference in body size. Finally, SSD develops well in advance of female reproduction in a high-altitude population with delayed maturation.

Food-deprivation affects tongue extrusions as well as attractivity and proceptivity components of sexual behavior in the lizard, Sceloporus jarrovii

AbstractExperiments were conducted to assess the effect of various levels of food deprivation (1, 2, 3, or 4-day periods) on tongue extrusions as well as attractivity and proceptivity components of sexual behavior in the sceloperine lizard Sceloporus jarrovii. Results showed sex differences with respect to effects of food deprivation on the attractiveness of male and female lizard odors toward conspecifics (attractivity). Males spent more time extruding their tongue to touch blocks containing odors of ad libitum-fed females as compared to odors from females deprived of food for 4 days, while spending a similar amount of time investigating blocks containing odors of ad libitum-fed females and females deprived of food for less than 4 days. In contrast, females spent similar amounts of time investigating odors associated with ad libitum-fed as well as food-deprived conspecifics. Results also showed that one day of food deprivation was sufficient to inhibit the desire to initiate or maintain contact with opposite-sex conspecifics (receptivity).

Discovery of an α-melanotropin antagonist effective in vivo

A hybrid analogue, H-His- d-Arg-Ala-Trp- d-Phe-Lys-NH 2, was designed based upon the primary structures of a growth hormone-releasing peptide analogue, [His 1,Lys 6]GHRP, and the MSH fragment, Ac-α-MSH(6–11)-NH 2. In vitro studies demonstrated the α-MSH antagonistic efficacy of the analogue in the lizards Sceloporus jarrovii and Urosaurus ornatus. In live white background-adapted S. jarrovii previously injected with the antagonist (10 nmol/5 g b.wt.), maximal skin darkening induced by α-MSH was reduced to 50%. In white background-adapted U. ornatus, previous injection of the analogue (1 nmol/5 g b.wt.) totally abolished the response to α-MSH and depressed to 50% the maximal response elicited by the superpotent MSH analogue, [Nle 4, d-Phe 7]α-MSH.

Gastrointestinal Helminths of the Yarrow Spiny Lizard, Sceloporus jarrovii jarrovii Cope

-The gastrointestinal tracts of 489 yarrow spiny lizards Sceloporus jarrovii jarrovii contained three nematode species: Physaloptera retusa, Spauligodon giganticus, Thubunaea sp.; two cestodes: Mesocestoides sp., Oochoristica scelopori and a juvenile acanthocephalan, Acanthocephalus sp. All are new host records. Spauligodon giganticus was the most prevalent parasite (prevalence 93.9%). Physaloptera retusa, Thubunaea sp., Oochoristica scelopori, Mesocestoides sp. and Acanthocephalus sp. had prevalences of 34.2%, 3.3%, 9.6%, 3.1% and 0.6%, respectively. The parasite load, measured as number of species present, is similar to that for other sceloporine lizards.